The purpose of the papers by Fox et al. (2017) and Potts (2017) is to clear up some of the empirical and conceptual confusion surrounding urbanisation on the continent. They seek to provide hard-headed assessments of changing urban patterns and dynamics. Key questions include: is urbanisation accelerating or slowing; how is the process affected by shifting economic conditions; and are (ungovernable) megacities growing more quickly than secondary cities and towns? These are weighty issues with far-reaching consequences for the sustainability of Africa���s urban growth and for the quality of life. An immediate difficulty revealed by both papers is that countries define and measure urban centres in different ways, using various criteria and size thresholds. In some places these categories have also been altered over time and in arbitrary ways, raising suspicions of interference to divert resource allocations towards favoured regions. This creates real problems for comprehending what is happening and embarking on policies to manage urban development more effectively. Inconsistent urban definitions yield different portraits of the national urban system, different accounts of rural���urban migration, and different interpretations of how territories are being reshaped. Incompatible definitions also complicate cross-country comparisons and confound efforts to develop more general understandings of urban growth dynamics. Urbanisation itself is also defined differently, sometimes going beyond the commonsense net shift in the population from rural to urban areas, to include the overall growth in the urban population and even the physical expansion of urban centres (Fox et al., 2017). International and domestic analysts alike rely heavily on population census data, but censuses are infrequent in many places, so the basic information for future projections can be very old. Fortunately the situation is beginning to improve with the increasing availability of satellite imagery and more regular household surveys in many nations.
Human Sciences Research Council (Sat,) studied this question.